Referring to FIG. 8, a conventional servo control system which is disclosed in Japanese Laid-Open Patent Publication No. 9-269811, will be explained.
In FIG. 8, the servo control system is constituted by a host CPU 6 which outputs controlling instructions to the entire system as an upper controlling unit, a plurality of servo-CPUs 8, 9 which executes the same calculations as the host CPU 6 and serve as lower controlling unit, drivers D1 to D3 which are connected to the servo-CPU 8 and also connected to servo motors M1 to M3 of an orthogonal-type robot (Cartesian type robot) 15, and drivers D4, D5 which are connected to the servo-CPU 9 and also connected to servo motors M4, M5 of a joint-type robot 17.
To the host CPU 6 are connected a key board 10 through which positional data for positioning points, for example, are inputted, an instruction device 11 for giving instructions about positional data as to positioning target points, and an external input-output circuit 13 that allows transmitting and receiving operations to or from an external device.
The following description will discuss an operation of the servo-control system having the above-mentioned arrangement shown in FIG. 8.
Upon starting an interpolation controlling process, the host CPU 6 transmits operating instructions for the next target point etc., to the servo-CPUs 8 and 9, and then the servo-CPUs 8, 9 execute the same calculations respectively for the synchronous control. Based on the result of the above calculations, the servo-CPUs 8, 9 execute the position feed-back controlling calculations of the respective servo-motors M1 to M3, M4, M5 to transmit positioning completion instructions to the host CPU 6.
In the above-mentioned servo control system, the respective servo-CPUs 8, 9 to which operating instructions are transmitted from the host CPU 6 can execute the same calculations respectively to carry out the synchronous control among the robots 15 and 17. Therefore, the above-mentioned system provides an effective control system for synchronous control when the number of controlled axes is comparatively small.
However, in a servo control system in which a number of motors are synchronously controlled among the respective servo-CPUs 8, 9 for interpolation controls, for example, in a servo control system for driving a tire molding machine with a number of control axes, as will be described later, the calculation time required in the respective servo-CPUs 8, 9 increases as the number of motors to be synchronously controlled increases, when each servo CPUs 8 and 9 need to execute the same calculations. This results in a longer interpolation controlling time.
In order to solve this problem, utilization of those servo-CPUs 8, 9 with a higher processing speed is recommendable, however, there is an inevitable limitation to the processing speed. Here, in the case when respective motors are mutually subjected to an interpolation controlling process, with respect to multiple axes M1–M5 as shown in FIG. 8, these are simply shown by two axes form, that is, X-axis and Y-axis as shown in FIG. 9.
In FIG. 9, the interpolation controlling calculations consist of synthetic locus calculations for calculating a length Lt1 on an interpolation line and respective-axis calculations for calculating positions Xt1 and Yt1 of the respective axes based on the length Lt1 on the interpolation line. Since the synthetic locus calculations are expected to be common to the respective motors, there is no need for the respective servo-CPUs 8, 9 to execute the same synthetic locus calculations, respectively.
Therefore, it is possible that either one of the servo CPU 8 (9) executes the synthetic locus calculations, and the other respective servo CPUs 8, 9 execute respective-axis calculations using the resultant value of the synthetic locus calculations.
However, the respective servo CPUs 8, 9 can not execute the respective axis calculations while one of the servo CPU 8 (9) is executing the synthetic locus calculations, therefore, the total interpolation-control processing time which is the sum of the synthetic locus calculation time and respective axis calculation time is not substantially reduced.
The present invention has been made to solve the above-mentioned problem in the servo-control system which carries out an interpolation control of respective axes of motors, and the object of the invention is to provide a servo control system and a control method thereof which can decrease the interpolation-control processing time of this entire system among two or more controllers without using CPU with a higher processing speed.